Generally speaking, most of the biodegradation studies and treatments are done in reactors (Jafvert and Rogers 1991). The largest reactor is a Dutch system where a mobile aerator moves along the treatment pond to maintain oxic conditions (Van Veen and Annokkee 1991). Other large treatments include landfarming (Van Dillen 1991) and the excavation and construction of a hill of contaminated soil with drainage tiles, nutrient dosing and sprinkler systems (Litchfield et al. 1992). These systems all require that the sediment be dredged and processed in sites which can involve the potential problems of security, cost, and public acceptance.
Some soil reclamation using biodegradation has occurred without excavation. The success of these treatments has varied greatly (Lee et al. 1988). Some contaminants cannot be readily biodegraded. Some treatments may not have provided the right environmental conditions for the microbes to completely biodegrade the organic wastes. Most of the failed bioremediation treatments in groundwater are related to either poor access to the wastes or to the blockage of the aquifer by the enhanced growth of microbes. The latter two problems do not apply to lake sediment on a macroscale; however, all sites can contain some polynuclear aromatic hydrocarbons (PAHs) locked in microsites which are therefore not biodegradable (Van Dillen 1991). Presumably these refractory PAHs would not be toxic. In similar studies it was found that coal dust contains PAHs but relative to coal tar and creosote, it is biologically inert (Alden and Butt 1987).
Bioremediation of groundwater and soils is a growing industry. As long as the treatment is preceded by an analysis of the treatability and toxicity of the site, it is a promising remedial option. Some toxins cannot be treated by biodegradation, but the cost of assessment is justifiable in that a detailed preassessment is substantially less expensive than excavation and chemical or physical treatment.
Bubbling the water column with oxygen has been proposed as a method of oxygenating the sediment (Murphy 1990). Some lake aeration treatments in Germany successfully oxygenated sediments but treatment with pure oxygen of some lakes in Switzerland did not oxygenate sediments (Gachter 1987). The engineering techniques are not completely developed, the treatment time may be long, and recovery difficult to predict accurately.
Further prior methods for treating sediment of sludge include the method of decontaminating wastewater sludge taught by Nicholson in U.S. Pat. No. 4,781,842. Reference is made to the use of lime, cement kiln dust and lime kiln dust for treating biological sludge. The goal of the treatment is to fertilize agricultural land. The reference does not address the problem of treating sludge associated with a water body for the purpose of enhancing natural microbiological degradation.
U.S. Pat. No. 5,008,020, discloses the use of a metal carbonate and a metal bicarbonate for solidifying waste material into a granular particulate form. The patentees do not discuss the merits of oxidation biodegradation inhibitors in order to effect more efficient biodegradation.
Conover, in U.S. Pat. No. 5,039,427, teaches a method for removing suspended solids and to precipitate and inactivate phosphorus in lake water by adding aluminum hydroxide sulphate. The reference does not discuss oxidation of sulphide to sulphate to reduce inhibition of natural microbial biodegradation.
U.S. Pat. No. 4,877,524, teaches an apparatus for treating bodies of water for correcting chemical, biological or other imbalances. The reference primarily relates to dispensing a treatment agent within a water body, the dispensing rate being proportional to the boat speed. Both aluminum sulphate and sodium aluminate are taught as treatment material among others. There is no provision in the apparatus for injecting or otherwise contacting the sediment with biochemical oxidant and accordingly, no contemplation for enhancing the natural microbial degradation of the sediment and more particularly the toxins of the sediment.
A further apparatus which is known in the art and which is directed to an apparatus for spraying plants is taught in U.S. Pat. No. 1,348,038, issued Jul. 27, 1920 to Neumeyer. When the disclosure of the Neumeyer reference is fully considered, it is clear that the apparatus in no way was intended for use within a thick and often viscous material such as sediment. Neumeyer's arrangement provides branched pipes which are arcuated shaped and include a nozzle, however, it is clear that they are connected to a main branch pipe by a fitting. Further, the terminal end of the branch pipe is connected to a fitting and subsequently to a main support beam. According to the Neumeyer apparatus, it would appear that the arcuate pipes are fixedly secured to the overall apparatus at two distinct points and, accordingly, it would appear that flexibility such as would be required when the apparatus encountered branches, trunks of trees, thick sediment rocks etc., would not be possible.
The Neumeyer arrangement further provides shares or lifting devices which travel in valleys between the crests of soil. Accordingly, it is clear that the apparatus is adapted for use on a surface which has a preformed trough within which the shares or lifting devices can travel. The shares are designed to travel on the ground and maintain the points of the shares either on or slightly above the surface of the ground and in position to engage under fallen or trampled portion of vines. Furtherstill, the Neumeyer disclosure indicates that lifting members are designed so that they do not dig into the ground but will underride vines and lift them to an appropriate height.
As a further limitation in the Neumeyer reference, the system is designed such that the fluid transportation members are the same members which would experience the force realized when debris, thick sludge or sediment etc. is encountered. It would be more desirable to have a separate support system for digging into the soil, which support system would support a separate means of transmitting a treatment fluid into the sediment.
Shuck et al. in U.S. Pat. No. 4,268,398, teach a method for rendering a sludge deposit in a waste water treatment facility into a pumpable mixture for relocation. This reference does not discuss an in-situ procedure for natural biodegradation of the sludge.
Further generally related references include U.S. Pat. No. 5,055,204 and Canadian Patent Application Nos. 2,007,455 and 2,016,310.
In view of the prior art, there exists a need for a sludge treatment process capable of being performed in-situ without stirring up the sediment into the water column and which permits a relatively large area to be treated quickly.